This invention relates to absorbent materials and in particular to absorbent materials wherein a formed fibrous substrate has deposited thereon a solution or dispersion of monomers and then is subjected to irradiation whereby said monomers polymerize in-situ, within the matrix of the fibers of the substrate. The resulting polymers are highly hydrophillic and greatly add to the absorbancy of the substrates.
Such absorbent materials may be employed in a wide variety of products and, in particular, in products for absorbing body fluids such as diapers, wound dressings, sanitary napkins, tampons, incontinent pads and the like. A method of making such absorbent materials is described in co-pending U.S. patent application Ser. No. 149,215, filed on May 12, 1980 by P. H. Ericksen, et al.
While each of these prior suggestions have produced a highly absorbent material well suited for use in the products being considered herein, the material still suffers, to a degree, from drawbacks inherent in the use of highly hydrophillic polymers. Specifically, it has been found that when such polymers become wet with fluid there is a tendency to form an occulsive film over the surface of the polymer particle, thereby precluding or at least greatly inhibiting, further penetration of liquid into the interior of the particle. The result is that while these polymers ultimately exhibit a high maximum capacity to absorb liquids, it takes a substantial time interval to reach this high capacity.
The art is now replete with suggestions for reducing this time interval including for example widely dispersing the polymers throughout a matrix of rapidly wicking material e.g., cellulose fiber webs, and controlling the particle size of the polymers. Most recently, in the above described patent application and patent, in-situ polymerization has been suggested for improving the distribution of hydrophillic polymers within an absorbent web and thereby decrease the time interval to attain maximum capacity.
While, in the main, each of the prior suggestions have in fact reduced the time interval for attaining maximum capacity, it is still highly desirable that further reduction be attained.